I have narrowed down this topic by deciding to write about the cost of lethal injection versus the cost of life imprisonment.
Hi Sarah, this will make it difficult. Using this theme will make it so that your whole essay is based on only one point.
The thing to do is write a few paragraphs about what each author says and then let your thesis take form after you have written lots of paragraphs. Always be willing to adjust your thesis at the end, because that allows for you to improve your perspective through research.
I recommend this one a lot:
"No, capital punishment is not morally required: deterrence, deontology, and the death penalty."(response to article by Cass R. Sunstein and Adrian Vermeule)
That article, if you can find it, has an introduction that outlines the whole argument as it usually takes form.